Electrical power supply networks, or “grids”, are generally arranged as illustrated in FIG. 1. Each home or business 110 has a master connection 120 to a mains electricity supply, through which all the electrical devices 111 in the home or business can be powered. A meter 130 can be connected between master node 120 and transmission grid 140 to monitor electricity usage by home or business 110. Meter 130 can report back to electricity supplier 150. Electricity supplier 150 has a server 151 at which they store account information for home/business 110. The electricity supplier uses usage data received from meter 130 to determine an amount to bill the account holder and issues them with a bill, for example via post or email or through an online portal. If the account holder fails to pay their bill, the electricity supplier may cut off supply to master node 120. However, the electricity supplier may not be able to recover the cost of the electricity already supplied.
Usage reporting from electricity meters is sometimes done via power-line communication (PLC). Several different PLC standards have been developed, including for example CAN-bus/LIN-bus over power line, SAE J1772 committee, IEEE 1901, ITU-T G.hn/G.996 etc. These are all schemes to modulate the alternating current (AC) mains signal to encode messages.
In situations where multiple end users may make use of electricity from a single master node, for example an electric vehicle charging point at a public parking space or multiple households or businesses housed in a single building, additional apparatus may be installed by a middle-man (e.g. a local council or a building management company) to re-sell electricity purchased from the supplier to individual users. This apparatus ensures only users who have pre-paid for their electricity (or have been authorised to use electricity from the master node for some other reason) gain access to it. Such apparatus may be an unattended point of sale (POS) terminal to which the end users supply payment, whether by inserting coins or notes or providing payment account details, e.g. by presenting a credit or debit card. Alternatively or additionally, such apparatus could check the user's identity, for example by them providing identification data or through biometrics.
An example of such an arrangement, as used for electric vehicle charging points, is illustrated in FIG. 2. The back end of the grid, i.e. electricity supplier 250 with server 251, transmission grid 240, meter 230 and master node 220 are all connected as in FIG. 1. In this case however, the account information held at the server is for the provider/maintainer of POS 260, for example a municipal council or car park management company. The end user plugs their vehicle 210 into a socket of POS 260 and provides payment credentials through a user interface 261 (e.g. by inserting a chip card into a card slot and entering their personal identification number (PIN) in a keypad). The POS checks the credentials (for example using an internet connection to a card issuer via a payment network, not shown) and switches on the socket into which the vehicle is plugged in response to receiving approval of the credentials.
This type of arrangement requires the end user's time to provide their credentials. It also requires the introduction of dedicated POSs to environments where they may not be desirable, e.g. due to lack of space or the local population finding them unattractive or inconsistent with the aesthetic of the locale. It also involves costs for the electricity re-seller for the acquisition, installation and maintenance of the POS. Therefore electricity re-sale POSs may not be installed at all in locations where a private re-seller could not profit from them and/or a public or charitable re-seller could not afford to subsidize them. For example, re-sale POSs may not be provided in remote locations where public charging points are desirable since those travelling to such locations are unlikely to have access to any private charging facilities in the vicinity, if any even exist. POSs may also not be provided in locations, e.g. in developing countries, where only a low proportion of the population can afford electrical devices and power for them. Access to “pay as you go” electrical power is especially desirable to such populations due to the reluctance of electricity suppliers to provide conventional credit-based electricity supply accounts to those with low and/or fluctuating incomes.
Some electrical power supply networks allow for account holders to offset their electricity bills, or even earn cash-back or other rewards, by selling electricity generated by private generator devices to the grid. For example a home or business with one or more solar panels or wind turbines or a geothermal energy extraction system can have a bi-directional trade relationship with an electricity supply company. However, to benefit from this arrangement, the account holder must connect their generator devices to the master node of their home or business, which may not always be possible. For example, electrical energy generated by the solar panel of a parked electrical or hybrid vehicle in excess of what its battery is capable of storing cannot be sold to the grid while away from home.